1. Field of the Invention
This invention relates to drive belts and in particular to toothed drive belts.
2. Description of the Prior Art
One form of conventional drive belt comprises a cog, or toothed, belt having a longitudinally extending body portion and a plurality of longitudinally spaced teeth projecting from the body portion. The teeth are adapted to be received in grooves of a toothed pulley for effecting a positive, nonslip connection therebetween. As a result, such belts may be used without lubrication as is required with conventional gear wheel drives and chain drives.
A problem, however, has arisen in the use of such toothed belts relative to interference between the belts and pulley during engagement and disengagement of the teeth so as to result in shortened useful life. More specifically, such interference may produce undesirable friction and cracking of the belt at the tooth roots.
One attempted solution to the wear problem has been to form the belt with trapezoidal teeth and to form involute pulley grooves. An example of such a belt is shown in U.S. Pat. No. 3,404,576. Such toothed belts, however, have been found to result in short life due to constant pressure exerted onto the belt tooth flanks in operation.
Another attempted solution to the problem is disclosed in U.S. Pat. No. 3,117,460. However, the belt disclosed therein does not fully satisfactorily solve the problem because of elongation of the tensile members, permitting the tooth-to-tooth pitch of the belt to increase in use. Resultingly, hard stress forces are generated on the roots of the teeth, resulting in cracks.